Avian erythroleukemia is a naturally occuring neoplastic disease of chicken, affecting the immature blood cells. The natural causative agents are avian leukosis viruses (ALV) which belong to a group of "non-transforming" retroviruses. These viruses do not encode oncogenes of their own, but can activate host oncogene by integration at an adjacent chromosomal site, thereby triggering the transformation process. The physical linkage of ALV DNA to the putative host oncogene in tumor DNA provides a molecular handle to identify the oncogene in erythroleukemia. Using molecular cloning, restriction enzyme digestions, blot-hybridization and other molecular biological approaches, we wish to (a) define the nature, the strucuture and the expression of the host oncogene for avian erythroleukemia, (b) characterize the mechanisms by which ALV activates the oncogene, and (c) study the effect of leukemic transformation on erythroid-differentiation. Our preliminary results are especially encouraging: we have identified a putative host oncogene, c-erb, for avian erythroleukemic transformation. Part of the proposed research is developed from this finding. Scientific discipline: Molecular Virology, Molecular Biology.